Circuit substrate and its manufacturing method

ABSTRACT

A circuit substrate has a flexible thin film, electric wires supported on the film, and an electric component supported on the film and positioned between the wires so that the wires and the components are electrically connected serially. Also, a thickness of the component is less than that of the electric wire.

FIELD OF THE INVENTION

[0001] The present invention relates to an electric circuit substrate. Also, the present invention relates to a film-like electric circuit substrate, e.g., an thinned integrated circuit substrate, for use with an electric device or an optical device, including a multi-layered electric circuit and functional modules mounted on the circuit. Further, the present invention relates to an electric circuit substrate with a plurality of layered circuit modules each having a flexible circuit boards and connections integrally formed with the boards for connecting the boards.

BACKGROUND OF THE INVENTION

[0002] Small sized electronic circuits with a high performance have been developed so far. In particular, a multi-function electronic circuit capable of being mounted in a small space has been provided for cellular phones and computers, for example. Simultaneously, further improvements have been made for an effective heat radiation from the circuits and for downsizing thereof.

[0003]FIG. 5 shows a part of the cellular phone. The cellular phone has a housing 21 in which a circuit board 22 or substrate is received. The circuit board 22 supports a plurality of electronic parts 23, a microprocessor (MPU) 24, a speaker 25 and a microphone 26 mounted thereon. With this cellular phone so constructed, a signal received by an antenna 27 is processed at the microprocessor 24, then transformed into an audio signal by the electronic parts 23, and finally transmitted from the speaker 25 in the form of voice. On the other hand, voices collected at the microphone 26 is transformed in a corresponding voice signal, then processed at the electronic devices and the microprocessor 24 and finally transmitted from the antenna 27.

[0004] Disadvantageously, the downsizing of the electronic devices requires an elevated performance of heat radiation for the circuit board. This problem may be solved by an enlargement of the circuit, which results in an enlargement of the phone. On the other hand, it is impossible to reduce an area of the circuit board less than that of the electronic devices. In addition, the currently used circuit board 22 and electronic devices 23 are relatively large in thickness. Those circumstances provide a great difficulty on the downsizing of the cellular phone and result in an increase of its manufacturing cost. To solve such problems, another idea may be proposed to layer a plurality of circuit boards. However, this requires longer wires for the electric connection of the electronic parts, which results in a difficulty in its jitter control.

[0005] Meanwhile, a double-sided circuit board bearing circuits on opposite surfaces and a multi-layered circuit board have been used for the compactness and the high performance of the circuit substrate of the electric and optical devices. In fact, a high density, multi-layered substrate are employed in a large number of electric devices.

[0006] In a process for manufacturing the multi-layered substrate, a glass cloth is impregnated with epoxy resin and then dried to produce a substrate material typically called as “prepreg”. Opposite surfaces of the prepreg is covered with copper film on which a dry film is then laminated. The dry film is exposed to light and then developed to form an etching pattern with which the copper film is etched. Finally, the dry film is removed from the prepreg to result in the double-sided circuit board. The double-sided circuit boards and the prepregs are layered alternately and then integrated by heating and pressing into the multi-layered circuit board. Subsequently, holes are defined in the multi-layered circuit board as necessary. Also, an electrically conductive layer is deposited on the inner surface of each hole, causing the electrically conductive layers mounted in the circuit board are electrically connected with each other.

[0007] On the surface of the multi-layered circuit board so constructed, a variety of functional parts are mounted to form a specific circuit. Typically, semiconductor chips including LCR for signal processing and also one or more packaged logic devices for calculation are mounted on the surfaces of the multi-layered circuit board. Further, in order to add another functions required for the electronic and optical devices, a plurality of multi-layered circuit boards can be connected with each other to form a certain module. Furthermore, a certain function module and/or power circuit may be connected for the transformation of the electric, optical and/or audio signal into the necessary information required for the device.

[0008]FIG. 9 shows a conventional electric/optical device using the multi-layered circuit board and the function modules. As can be seen from the drawing, the device has a multi-layered printed circuit board 231, a flexible board 232, a liquid crystal module 233 a, an optical camera module 233 b, an input touch panel module 233 c, a packaged logic circuit 234, a chip-like function component 235, a copper wire 236 defined in the multi-layered circuit board, and through-holes 237 each filled with an electrically conductive paste for electrically connecting the circuits on respective layers.

[0009] In operation of the device using the multi-layered circuit board, optical information is captured and then transformed into a corresponding electric signal by the optical camera module 233 b. The signal is processed into image data by the logic circuit 234 on the bottom surface of the board. Another information inputted through the touch panel 233 c is also transformed into a corresponding electric signal which is then processed by the chip circuit components on the bottom surface of the board, for example. Those information is then transformed into respective signal data which is transmitted through the flexible circuit 232 to another multi-layered circuit board where it is further transformed by the logic circuit 234 and the function components 235 such as LCDs. Subsequently, data so transformed is transmitted through the flexible circuit 232 to the liquid crystal module 233 a where it is transformed into a corresponding optical signal and then displayed in the form of image.

[0010] As described above, the functional devices and components mounted on the opposite surfaces of the multi-layered circuit board are electrically connected by various wires mounted within and/or between the layers. Also, the copper wires 236 (circuit pattern) of respective layers and the electrically conductive paste 237 filled in the through-holes for the connection of the copper wires 236 are electrically connected with each other to form a three-dimensional circuit.

[0011] However, in this three dimensional circuit, the function components are mounted only on each surface of the layers. This results in various difficulties on the shortening of the wires between the components and/or modules and requires a flexible circuit board, for example, for the electric connection of the layers, which may cause an adverse affects such as loss and/or noises in the transmission of the high frequency signals. Also, the chip components and packaged function devices are connected to the board by soldering, for example, which makes it difficult to increase a performance of the overall circuit due to possible inaccuracies of the component and its mounting. This further provides a great difficulty on the manufacturing of a high-frequency, high-speed and digital device and then on its downsizing and high-functionalization.

[0012]FIG. 13 shows a flex-rigid circuit board 301. The board 301 has an unfoldable rigid portion 302 and a foldable flexible portion 303. The flexible portion 393 supports a multi-layered circuit board 304 bearing a conductive circuit 305. The conductive circuit 305 is covered by a protection film 306 bonded thereon. In the rigid portion 302, a rigid circuit board 308 is layered on and bonded with the multi-layered circuit board 304 using a bonding sheet and/or prepreg 307. Also, in the flexible portion 303 where the multi-layered circuit board 304 is exposed, the bonding sheet and/or prepreg 307 and an associated part of the rigid circuit board 308 are removed therefrom. A plurality of electronic components 309 are mounted on the rigid circuit board 308 of the rigid portion 302. Those components 309 are electrically connected by through holes 310 running through the multi-layered circuit board 304 and the rigid circuit board 308.

[0013] As described above, the conventional flex-grid circuit board 301 lacks the flexibility in a region made by the multi-layered circuit board 304, which results in a great difficulties on a configuration of the circuit board and then on its installation into a housing with curved portions. Also, the multi-layered circuit board 304 has a certain thickness which prevents the shortening of the wires in its direction and fails to meet the high-frequency requirement. Further, a number of through-holes should be arranged in a complex manner for the connection of the layered circuits, which provides various restrictions on the circuit design and the downsizing of the circuit board, for example, and increases the manufacturing cost of the circuit board.

[0014] In the meantime, according to the conventional multi-layered circuit board, each layer is fully bonded with the adjacent. Also, only after the completion of the manufacturing of the circuit board, a test is made to confirm whether each layer operates in an expected manner. This is because it can be thought that the multi-layered circuit board works well only after all the layers have been fabricated and then connected with each other. This means that no operation test could be made until the completion of the manufacturing of the multi-layered circuit board, which makes it difficult to determine or remove the defective products in the process of manufacturing, which results in a decrease of the yield rate and makes the products costly.

SUMMARY OF THE INVENTION

[0015] According to the present invention, an electric circuit substrate has a flexible thin film, electric wires supported on the film, and an electric component supported on the film and positioned between the wires without any overlap with the wires so that the wires and the components are connected serially and a thickness of the component is less than that of the electric wire.

[0016] In another aspect of the present invention, a circuit substrate has a plurality of films layered one on top the other, each film supporting electric wires and an electric component electrically connected between the wires, wherein wires on one film and those on other film are electrically connected with each other through a connection running between opposite surfaces of the one or the other film.

[0017] In another aspect of the present invention, a circuit substrate has a plurality of layers each of which being selected from any one of a first organic film supporting a circuit with a function module, a second organic film supporting a thinned function circuit, and a third organic film supporting a bare chip function device, the circuits on the layers being electrically and/or optically connected with each other.

[0018] In another aspect of the present invention, a circuit substrate which is incorporated within a cellular phone, personal data assistant, computer, identification card, electric wallet, remote controller or memory card, wherein the substrate has a plurality of layers each of which being selected from any one of a first organic film supporting a circuit with a function module, a second organic film supporting a thinned function circuit, and a third organic film supporting a bare chip function device, the circuits on the layers being electrically and/or optically connected with each other.

[0019] In another aspect of the present invention, a circuit substrate has a plurality of circuit modules layered one on top the other. Each of the circuit modules has two flexible circuit boards each supporting components for transmitting or processing a signal and a circuit for connecting the components, and a flexible connecting portion formed integrally with the two flexible circuit boards and supporting a circuit for electrically and/or optically connecting the circuits on the circuit boards.

[0020] In another aspect of the present invention, a circuit substrate has a first circuit module and a second circuit module, each of the first and the second circuit modules having a first and a second circuit boards and a connection portion for connecting the first and second circuit boards, each of the first and second circuit board supporting a plurality of components for transmitting or processing a signal and a circuit for connecting the components, the connecting portion supporting another circuit for connecting between circuits on the circuit boards, wherein the first and the second circuit modules are layered so that the first and the second circuit boards of the first circuit module are layered on the first and second circuit boards of the second circuit module.

[0021] In another aspect of the present invention, a process for manufacturing a circuit substrate, the substrate having a plurality of circuit modules layered one on top the other, each of the circuit modules having a flexible circuit board supporting components for transmitting or processing a signal and a circuit connecting the components and a flexible connecting portion integrated with the circuit boards for electrically and/or optically connecting the circuit boards, comprises detecting an operation of the circuits supported on one or more circuit modules before a completion of layering of the circuit modules.

[0022] It should be noted that the present application is based upon three Japanese Patent Applications Nos. 2001-355415, 2002-019947 and 2002-086373, the entire contents of which being incorporated herein by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is an enlarged cross sectional view of a single-layer thinned circuit substrate according to the first embodiment of the present invention;

[0024]FIG. 2 is an enlarged cross sectional view of a multi-layer thinned circuit substrate according to the second embodiment of the present invention;

[0025]FIG. 3 is an enlarged cross sectional view of the multi-layer circuit substrate in FIG. 2 in which a part of the substrate is deformed;

[0026]FIG. 4 is an enlarged cross sectional view of the multi-layer circuit substrate according to the fourth embodiment of the present invention, in which a piezoelectric element is incorporated;

[0027]FIG. 5 is a perspective view of a part of a cellular phone;

[0028]FIG. 6 is an exploded perspective view of the thinned circuit substrate according to the fifth embodiment of the present invention;

[0029]FIG. 7 is a cross sectional view of the thinned circuit substrate in FIG. 6;.

[0030]FIGS. 8A to 8F show specific embodiments of the multi-layer film device;

[0031]FIG. 9 is a cross sectional view of a conventional electrical and/or optical device with multi-layer circuit substrate and function modules;

[0032]FIG. 10A is an exploded perspective view of the thinned circuit substrate according to the sixth embodiment of the present invention;

[0033]FIG. 10B is a cross sectional view of the thinned circuit substrate according to the sixth embodiment of the present invention;

[0034]FIG. 11A is another cross sectional view of the thinned circuit substrate according to the seventh embodiment of the present invention;

[0035]FIG. 11B is a cross sectional view of the thinned circuit substrate according to the seventh embodiment of the present invention; and

[0036]FIG. 12 is an exploded perspective view of the thinned circuit substrate according to the eighth embodiment of the present invention; and

[0037]FIG. 13 is a cross sectional view of a conventional flex-rigid substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] With reference to the drawings, various embodiments of the present invention will be described hereinafter. For clarity of the drawings, like parts are designated like reference numerals throughout the drawings.

First Embodiment

[0039] Referring to FIG. 1 showing an enlarged thinned circuit board 101 incorporated in an electronic device such as cellular phone. As shown in the drawing, the circuit board 101 has a base 102 made from a thinned flexile and foldable film. The film 102 has a number of thinned wires 103 on its one or both major surfaces formed thereon. A plurality of components 104 each having a thickness less than the wires 103 are also mounted on the film between the wires 103, i.e., beside the wires, so as not to overlap the wires. Preferably, the film of the base 102 is made of polyethyleneterephthalate (PET), polyimide, or polyphenylene sulfide (PPS). Also preferably, a thickness of the film is about 5-150 μm in order to provide a sufficient flexibility to the film. The film may be a metal film such as aluminum foil. When using aluminum foil, an insulation layer made of epoxy resin, for example, may be provided on its surface.

[0040] This insulation layer is not necessary if the surface of the film bears an oxide coating formed thereon.

[0041] The wires 103 are formed by forming a film of conductive metal on the surface or surfaces of the base 102 by the use of a known film formation technique such as physical and chemical vapor depositions and then etching the metal film. Preferably, a thickness of the film wire is equal to or less than about 3 μm. Although a copper having a high conductivity is preferably used for the metal material of the wires 103, another materials such as palladium, gold and silver may be used instead.

[0042] The components 104 includes capacitors, coils, resistors and transducers, for example, each of which is manufactured on the base 102 by the use of a known film formation technique such as physical and chemical vapor depositions typically employed in the manufacturing of the semiconductor elements. Alternatively! the thinned components already manufactured on another film may be positioned on the base 102 and then electrically connected with the associated wires 103 by soldering. Preferably, in any case, the thickness of the components is less than about 1 μm.

[0043] As described above, the thinned base 102 of the circuit board 101 according to this embodiment supports the thinned wires 103 of the elevated conductivity and the thinned components 104 which is thinner than the wires 103, which provides the circuit board 101 with the greater flexibility and then allows it to follow any configuration of the housing with ease. Also, the circuit board 101 can be accommodated within a smaller space than the conventional rigid circuit board, which allows further downsizing and light-weighting of the device. Also, when a portion of the circuit board 101 bears a component having a thick element such as speaker shown in FIG. 5, another portion of the circuit board surrounding the element is curved, allowing the circuit board with the element to be housed within a small space of the device.

Second Embodiment

[0044]FIG. 2 is also an enlarged cross sectional view of the thinned circuit board of the second embodiment. As shown in the drawing, a multi-layered circuit board 101A is manufactured by stacking a plurality of single-layer circuit boards 101 or layers of the first embodiment. Although the multi-layered circuit board 101A has three single-layer circuit boards in the embodiment, the number of the single-layer circuit board is not limited thereto. Preferably, the single-layer circuit boards are connected entirely or in part with each other by the use of an insulative adhesive or a suitable connector such as clip.

[0045] The components 104 mounted on one single-layer circuit board 101 can be electrically connected with those mounted on the adjacent single-layer circuit board 101 through electric connectors 105 defined in either of the two single-layer circuit boards 101. For example, the electric connector 105 has a through-hole 106 defined in the base 102 and a wire portion 107 formed on an inner surface of through-hole 105 or filled in the through-hole 105, which may be formed by the use of a known semiconductor manufacturing technique.

[0046] With this arrangement of the multi-layered circuit board 101A, for example, an electric signal from one component 104 on the top base 102 or layer is transmitted through the wire or wires 103 and then the electric connector 105 of the top base to another component 105 of the second layer. This ensures that the signal is transmitted through a shorter pass, when compared with the conventional circuit board in which signal is transmitted through another pass mounted on the edge of or around the circuit board. This prevents that the signal picks up possible unwanted noises and/or disturbances.

[0047] As described above, the thinned circuit board 101A of the present invention, which is made of thinned base 102 and the thinned components 104 mounted thereon, minimizes the number of components to be mounted on the base 102. This causes the circuit board 101A to be downsized, allowing the circuit board 101A to be housed within a smaller space and light-weighted.

Third Embodiment

[0048]FIG. 3 shows a housing 110 and a multi-layered circuit board 101B received in the housing. In this embodiment, the housing 110 has a surface 111 for receiving the circuit board. The receiving surface 111 has a deformation such as recess 112 or curved portion where at least one hole 114 extending between top and bottom surfaces, 111 and 113, of the housing.

[0049] In order for mounting the circuit board 101B in the recess 112 as illustrated, first a plate like circuit board 101B is placed on the surface 111 of the housing 110 so that it covers the recess 112. Then, a chamber defined within the recess 112 is connected to and then vacuumed by a suitable vacuum machine 115, so that the flexible thinned circuit board deforms by the vacuum pressure into the chamber to follow the inner configuration of the recess 112, providing the circuit board 101B with the three dimensional configuration corresponding to that of the recess 112.

[0050] If the circuit board 101B is easy to recover its original plane configuration due to its elasticity by the elimination of the vacuum, a peripheral edge of the circuit board 101B is preferably fixed continuously to the housing 110 by the use of a suitable bonding technique such as heat sealing 116 and adhesive. In this instance, the hole 114 is closed by heating and then deforming a housing portion surrounding and defining the hole or by filling a suitable bonding material in the hole, which permanently maintains the three dimensional deformed configuration of the circuit board. If the overall surface of the circuit board or at least a portion of the circuit board adjacent to the chamber of the housing 110 is smooth and does not support any component, no heat seal is needed. Also, if the circuit board 101B is deformed plastically beyond it elasticity limit, nothing is required for retaining the deformed condition. Further, the circuit board 101B may be deformed to a configuration corresponding to that of chamber before it is mounted on the housing.

[0051] As described above, the thinned circuit board is housed within the housing without any difficulty even when the housing has a convex and/or concave portion. This ensures that the housing or device receiving the housing is designed freely and also decreases a manufacturing time and cost. Also, the performance of the device is so improved.

[0052] Although the circuit board 101B is deformed by the use of vacuum, it can be done by a heat press in which the circuit board is heated and then deformed.

Fourth Embodiment

[0053]FIG. 4 shows another thinned circuit board 101C according to the third embodiment of the present invention. The circuit board 101C is featured in that a piezoelectric element 117 is incorporated in the circuit board so that it detects a deformation of the circuit board and then generates a signal corresponding the amount of the deformation. The piezoelectric element 117 is formed on the base 102 before or after the formation of the wires 103 on the base 102, by the use of a known film formation technique such as physical and chemical vapor depositions typically employed in the manufacturing of the semiconductor elements. Also, the single-layer circuit board in which the piezoelectric element 117 has been formed is stacked on another single-layer circuit boards each bearing required wires 103, components 104 and connectors 105 and then bonded, if necessary, to obtain the thinned circuit board 101C.

[0054] In operation of the circuit board 101C so constructed, if the base is deformed by any external force or energy, the piezoelectric element follows the deformation. In the piezoelectric element, the deformation is changed into a signal having a voltage corresponding to the amount of deformation, which is transmitted from the associated wire. If the force or energy is eliminated, the base returns to its original state and the output voltage of the piezoelectric element 117 returns to that before the deformation.

[0055] Therefore, the piezoelectric element 117 can be used as an audio component of the speaker and microphone. This means that the speaker and microphone can be downsized. On the other hand, the piezoelectric element 117 is used as a vibration generator or vibrator. In this instance, the piezoelectric device may be located on opposite sides of the axis so that it expands and contracts and thereby rotates about the axis in response to on/off operation of the voltage, minimizing a difference between the actual deformation and the calculated deformation derived from a deformation versus voltage relationship.

[0056] Although the deformation of the circuit board is detected by the piezoelectric device, it may be replaced by a spring switch, for example.

Fifth Embodiment

[0057] The fifth embodiments relates to another thinned circuit board, i.e., an integrated circuit structure made of film-like devices. The circuit board has film layers including at least one of three organic films, a first organic film supporting a circuit with at least one function module, second organic film supporting a thinned function circuit and a third organic film supporting a circuit with function devices like bare chips, in which the circuits on the films are electrically and/or optically connected with each other.

[0058] Referring to FIGS. 6 and 7, the circuit board has a plurality of films positioned one on top the other. The films includes an organic film 201 supporting function module circuits, an organic film 202 supporting thinned function components and bare-chip devices, an organic film 203 supporting function module circuits and thinned function circuits, a transparent protection film 204, a bonding film 205 and a protection film 206. In the drawings, the thinned function modules, the function circuit components and the bare-chip function devices are indicated by reference numerals 207 a-207 i, 208 a-208 c and 209, respectively. Also, metal connections for electrically connecting between circuits on different films are indicated by reference numeral 210.

[0059] The function modules may include a liquid crystal display 207 a, a receiver (or speaker) 207 b made of piezoelectric material, a thinned microphone 207 c, a CCD camera 207 d, a button 207 e such as touch panel, a light emitter 207 f such as LED, a thinned antenna 207 g for receiving a signal, a thinned battery 207 h and a thinned vibrator 207 i for generating vibrations.

[0060] In FIG. 6, the function modules 207 are positioned on the organic film 201 and 203 made of PET or polyimide and having a thickness of about 100 μm. Also, the organic film 201 supports modules having an audiovisual interface for operators, on top of which the protection film 204 is bonded. The components mounted on the organic film 201 transform electric and optical signals into corresponding audio signals and vice versa. Also, the circuits connecting between various function modules process necessary information.

[0061] The organic film 203 supports various function modules for supplying power to mobile terminals, receiving signals and generating vibrations, irrelevant to audiovisual operation of human beings. The bottom surface of the organic film 203 is covered by the protection film 206.

[0062] As shown in FIG. 7, in order to process and control signals to and from the function modules 207, the organic films are electrically connected by metal connections 210 such as metal bumps. Another portion except metal connections 210 are electrically disconnected from each other. Also, in order to connect the organic films, an organic material such as bonding film 205 is provided therebetween.

[0063] Each of the organic films 201, 202 and 203 may be made of a plurality of stacked films. In this instance, the bonding film 205 may be placed between the stacked films.

[0064] For the optical connection between layers, a transparent film may be provided entirely or partially between the layers so that light emitted from the light emitter such as LED is received by the light receiver such as photodiode.

[0065] The organic film 202 supports various function circuits such as function component or device for processing and controlling various signals. The function circuits includes a thinned capacitor 208 a, a thinned register 208 b and thinned inductor 208 c. Those function circuits 208 may be manufactured on the organic film 202 by a suitable film formation technique such as sputtering. Alternatively, the thinned function components may be prepared on another organic film, which are then separated from each other.

[0066] The function circuits are manufactured by forming one or more layers each having a thickness of less than 10 μm by the use of a known film formation technique and then patterning the layers. If the manufacturing needs a film formation process in which the circuit is exposed to an elevated temperature, a heat resisting material such as polyimide is preferably used for the organic film 202. The function device 209 may be a bare chip including semiconductors made of silicon and/or other chemical compounds. For example, the device 209 is IC and LSI capable of electrically performing a calculation or semiconductor device made of GaAs and/or other chemical compounds and capable of functioning as an optical circuit. The bare chip, functional device 209 is mounted on wires formed on the organic film 202 through metal connections such as bumps. For example, the device 209 has a thickness equal to or less than about 100 μm.

[0067] Using the circuits described above, constructed is the thinned mobile terminal device, i.e., the circuit structure shown in FIG. 7. As described above, since the multi-layered bases are made of thin and light film, the structure has a minimum thickness, equal to or less than about 7 μm, for example, and a minimum weight.

[0068] Although the structure of the film-like integrated circuit is applied to the mobile device (i.e.;, thinned cellular phone), it can be embodied as other thinned devices because of its minimum thickness of about equal to or less than 7 μm. As shown in FIGS. 8A to 8F, examples of the thinned devices are a sheet-like computer 241, an identification such as ID card 242, an electronic wallet 243, a personal data assistant (PDA) 244, a remote controller 245 and a memory card 246 for use with an electric device such as electric washer 247, television 248 and microwave oven 249.

[0069] The functions provided to the structure are not limited to those for mobile devices, but may be those required for the sheet type computer, sheet ID such as passport, license and name card, sheet memory for recording audio and visual data, sheet wallet such as credit card and season ticket and sheet-like remote controller.

[0070] As described above, according to the film-like integrated circuit structure, since the electric components and function circuits are electrically connected through the three dimensionally arranged electric wires, i.e., the connections defined in the layers and the wires formed on the layers, the length of the wires running between the functional components and modules can be minimized.

[0071] Also, the conventional flexible board for connecting between the multi-layered circuit board can be eliminated. Besides, the film base is so light, compared with the conventional multi-layered circuit board made of epoxy with glass fibers. This causes the circuit board to be light weighted.

[0072] Further, the metal connection such as bumps can be used for the connection between the layers and between the bare-chip devices and the associated circuits, which reduces a deterioration of high-frequency signals to a certain extent when compared with the conventional connection using the conductive paste material and thereby decreases a signal transmission loss.

[0073] Furthermore, since the multi-layered device employs the optical connection for the signal transmission between the layers, the optical signal from the optical device can be used as optical information, which considerably reduces an adverse affect caused by noises and allows a high speed and mass signal processing.

[0074] Moreover, the function circuits and bare-chip function devices made of thin films each having a thickness less than 10 μm are incorporated between the layers. Then, when compared to the circuit structure using chip components or package devices, a possible inaccuracy due to the mounting of those devices is eliminated, which improves the performance of the overall circuit.

[0075] Therefore, the present invention provides a compact multi-layer circuit device in which the operational signal frequency can further be increased and the signal can be transmitted in a high speed.

Sixth Embodiment

[0076]FIG. 10A also shows a thinned multi-layer circuit device according to the sixth embodiment of the present invention. As shown in the drawing, the thinned multi-layer circuit 311 has a plurality of circuit modules 312, i.e., layers, superimposed one on top the other. Each circuit module 312 has a first and a second rectangular circuit boars, 313 and 314, and a strip-like connecting portion 415 connecting between the first and second circuit boards. A base layer 316 defining the circuit module 312 is made from a flexible thin sheet made of insulative material. For example, the sheet is made from a flexible resin film or a metal film coated with an insulative material. The sheet is cut and configured so that it outlines both the first and second circuit boards 313 and 314 and the connecting portion 315. The circuit boards 313 and 314 supports necessary electronic and/optical components 317 such as resistors, capacitors, coils and LSIs. As required, the components 317 are electrically connected with each other through wires 318 made of metal film and defined on one or opposite surfaces of the circuit boards 313 and 314. The connecting portion 315, on the other hand, supports connecting wires 319 for electrically and optically connecting between the components 317 and wires 318 on the first and second circuit boards 313 and 314, as required. Other electrical and/or optical connections including through-holes (not shown) are formed in the circuit boards 313 and 314 and the connecting portion 315 for connecting wires 318 in one layer and another wires 318 in other layers.

[0077] In this embodiment, the circuit boards 316 of the circuit modules 312 have the same configuration so that, once the modules 312 are superimposed, the first and second circuit boards 313 and 314 and the connecting portion 315 in one circuit module 312 are correctly aligned on those of adjacent circuit module 312. The electronic components 317 and wires 317 and 318 on one circuit module 312 need not to be identical to those on other circuit modules. Typically, each circuit module 312 bears components and wires different from those of other modules.

[0078] As shown in FIG. 10B, the circuit modules 312 so formed are superimposed so that the first and second circuit boards 313 and 314 and the connection portion 315 are positioned on those of others. Also, the superimposed circuit connections 315 are then pressed and integrated, which results in the thinned multi-layer circuit 311. If necessary, a suitable adhesive is used for bonding at least respective parts of the superimposed circuit boards and/or connecting portions. Preferably, a bonded area of each circuit board is equal to or less than 50% of the total area of the circuit board for an effective heat radiation from an interference between the superimposed circuit boards and also for retaining a good flexibility of the multi-layer circuit.

[0079] The electric wires 318 and 319 of each circuit module 312 are electrically connected with associated wires of other circuit modules through the electric connections or through holes defined in the circuit boards 313 and 314 and/or the connecting portions 315. This means that the circuit boards 313 and 314 superimposed are electrically connected only through such connections, allowing heat generated in the circuit boards 313 and 314 of the circuit modules 312 to be discharged into the atmosphere through possible small gaps between unconnected portions of the circuit boards.

[0080] As described above, the integrated thinned multi-layer circuit 311 still has a significant flexibility so that it can be bent or curved so easily, allowing the circuit to be accommodated within a housing with any configuration having convex and/or concave portions.

Seventh Embodiment

[0081]FIG. 11A shows another thinned multi-layer circuit device 311A according to the seventh embodiment of the present invention. As shown in the drawing, the multi-layer circuit device 311A of this embodiment is different from that of sixth embodiment in that the connecting portion 315 of one circuit module 312 takes a specific position relative to its circuit boards 313 and 314, so that, when the circuit modules 312 are superimposed, the connecting portion 315 in one module takes different position from those of other modules.

[0082] Therefore, as can be understood when comparing the multi-layer circuits shown in FIGS. 11A and 10A, although the connecting portions 315 in the multi-layer circuits 311A takes a large area than that of the previous embodiment, a thickness of the connecting portions in the multi-layer circuit is far smaller than that of the previous embodiment. For example, if the connecting portions are arranged so that they have no overlap with each other, the thickness of the connecting portions in the multi-layer circuit board corresponds substantially to that of single connecting portion. This results in a significant flexibility of the multi-layer circuit board, allowing the circuit board to be designed more freely.

Eighth Embodiment

[0083]FIG. 12 shows another thinned multi-layer circuit board 311B according to the eighth embodiment of the present invention. Although the multi-layered circuit board 311B has a plurality of circuit modules 312 layered one on top the other like seventh embodiment, it is different from that embodiment in a layering order of the circuit boards. Specifically, in the left part of the multi-layered circuit, indicated on the left side of FIG. 12, positioned in the top layer is the circuit board 313 a of one circuit module 312 and in the second layer is the circuit board 313 b. On the other hand, in the right part of the multi-layer circuit board, indicated on the right side of FIG. 12, the circuit board 314 a is positioned in the second layer and the circuit board 314 b is in the top layer. That is, the layering order of the circuit boards is different in the left and right sides. For clarity, only one example is shown in the drawing in which the top two layers of the circuit boards 313 and 314 are exchanged, the layering order of the circuit boards can be modified freely. 

What is claimed is:
 1. A circuit substrate, comprising: a flexible thin film; electric wires supported on the film; and an electric component supported on the film and positioned between the wires so that the wires and the components are connected serially, wherein a thickness of the component is less than that of the electric wire.
 2. The circuit substrate of claim 1, wherein the circuit substrate has a plurality of layers each including the flexible film supporting the electric wires and the component.
 3. The circuit substrate of claim 1, wherein a thickness of the wires and a thickness of the component are less than that of the film.
 4. The circuit substrate of claim 1, wherein the film is made of resin or metal.
 5. The circuit substrate of claim 1, wherein the film is made of polyethyleneterephthalate, polyimide, polyphenylene sulfide or aluminum.
 6. A circuit substrate, comprising: a plurality of films layered one on top the other, each film supporting electric wires and an electric component electrically connected between the wires, wherein wires on one film and those on other film are electrically connected with each other through a connection running between opposite surfaces of the one or the other film.
 7. The circuit substrate of claim 1, wherein the substrate is transformed so that it has a three dimensional configuration.
 8. The circuit substrate of claim 1, further comprises an element capable of transmitting a signal corresponding to an amount of transformation.
 9. A circuit substrate, comprising: a plurality of layers each of which being selected from any one of a first organic film supporting a circuit with a function module, a second organic film supporting a thinned function circuit, and a third organic film supporting a bare chip function device, the circuits on the layers being electrically and/or optically connected with each other.
 10. The circuit substrate of claim 9, wherein the function circuit on the second organic film has a thickness of equal to or less than 10 μm and each organic film has a thickness of equal to or less than 100 μm.
 11. The circuit substrate of claim 9, wherein a metal connection is used for the electric connection of the circuits on the different layers.
 12. The circuit substrate of claim 9, wherein the second organic film supports a bare chip function device.
 13. The circuit substrate of claim 9, wherein function module transforms a signal in the form of an electric, optical or audio signal into another form of signal.
 14. The circuit substrate of claim 9, wherein the function circuit is a capacitor, inductor or register.
 15. The circuit substrate of claim 9, wherein the substrate has a thickness of equal to or less than 7 μm.
 16. A circuit substrate which is incorporated within a cellular phone, personal data assistant, computer, identification card, electric wallet, remote controller or memory card, wherein the substrate has a plurality of layers each of which being selected from any one of a first organic film supporting a circuit with a function module, a second organic film supporting a thinned function circuit, and a third organic film supporting a bare chip function device, the circuits on the layers being electrically and/or optically connected with each other.
 17. A circuit substrate, comprising: a plurality of circuit modules layered one on top the other, each of the circuit modules comprising two flexible circuit boards each supporting components for transmitting or processing a signal and a circuit for connecting the components, and a flexible connecting portion formed integrally with the two flexible circuit boards and supporting a circuit for electrically and/or optically connecting the circuits on the circuit boards.
 18. The circuit substrate of claim 17, wherein the circuit modules are layered so that the connecting portions do not overlap each other.
 19. The circuit substrate of claim 17, wherein at least two of the circuit modules are layered so that one of the circuit boards of one circuit module is positioned above one of the circuit boards of the other circuit module and the other of the circuit boards of one circuit module is positioned under the other of the circuit boards of the other circuit module.
 20. The circuit substrate of claim 17, wherein the adjacent circuit boards of at least two circuit modules are at least in part in contact with or bonded with each other.
 21. The circuit substrate of claim 20, wherein a contact or bonded area of the adjacent circuit boards is 50 % or less of an entire area of each of the circuit boards.
 22. The circuit board of claim 21, wherein the adjacent circuit boards are electrically or optically connected with each other in the contact or bonded area.
 23. A circuit substrate, comprising: a first circuit module and a second circuit module, each of the first and the second circuit modules having a first and a second circuit boards and a connection portion for connecting the first and second circuit boards, each of the first and second circuit board supporting a plurality of components for transmitting or processing a signal and a circuit for connecting the components, the connecting portion supporting another circuit for connecting between circuits on the circuit boards, wherein the first and the second circuit modules are layered so that the first and the second circuit boards of the first circuit module are layered on the first and second circuit boards of the second circuit module.
 24. The circuit substrate of claim 23, wherein the first circuit board of the first circuit module is placed on or above the first circuit board of the second circuit board and the second circuit board of the first circuit module is placed below or under the second circuit board of the second circuit module.
 25. A process for manufacturing a circuit substrate, the substrate having a plurality of circuit modules layered one on top the other, each of the circuit modules having a flexible circuit board supporting components for transmitting or processing a signal and a circuit connecting the components and a flexible connecting portion integrated with the circuit boards for electrically and/or optically connecting the circuit boards, comprising detecting an operation of the circuits supported on one or more circuit modules before a completion of layering of the circuit modules. 